“Don’t reheat rice” is one of those pieces of advice that everybody has heard at some time or another. But as with many pieces of advice from the modern era, it’s a little mired in disinformation.
Dried rice is often contaminated with Bacillus cereus spores, a bacterium related to B. subtilis (often used as a laboratory subject), and B. anthracis, which is responsible for causing anthrax. While anthrax bacteria cause massive tissue necrosis and death, B. cereus does little more than generic food poisoning symptoms – you know, nausea, vomiting, diarrhoea, all that juicy stuff. This illness is sometimes referred to as “fried rice syndrome” due to its propensity to emerge several hours after consuming a takeaway.[pullquote]If you leave your rice out for too long, you might as well eat a raw chicken breast for all the good it does you[/pullquote]
cereus is usually found in soil and can be transferred to rice plants. When rice is dried before packaging, B. cereus changes from their regular form to a spore – they “sporulate”, in other words. After all, any old bacterium will quickly dehydrate and die if there is no water available, but a spore can survive for years. Rice packaging will often tell you to rinse the rice before cooking, and one of the reasons to do so is that it helps get rid of some of the spores.
When rice is boiled, the water content would activate the spores if it weren’t for the high heat. Leaving the rice to cool down on the counter gives the bacteria plenty of time to leave the spore, start multiplying, and produce toxins. If you leave your rice out for too long (i.e. two hours or longer), you might as well eat a raw chicken breast for all the good it does you.
So when is it OK to reheat rice? Well, preferably not at 3am when you’re blind drunk and trying to make a snack, only to leave it in the microwave for too long, causing it to burn and set off the fire alarm… But besides that, whenever. As I may have implied from the preceding paragraphs, it’s not reheating the rice that makes it dangerous, but keeping it warm for hours.
In short, keep your rice above 60˚C (cooking temperature) or below 4˚C (fridge temperature) if you’re not going to eat it immediately. After cooling, you can reheat the rice in the microwave like any other foodstuff, no problem. Bone apple tea.